In general, a hermetic compressor includes a compression mechanism unit compressing refrigerant by a reciprocating motion, a motor mechanism unit supplying power to the compression mechanism unit, and a hermetic container accommodating the compression mechanism unit and the motor mechanism unit an airtight state. The hermetic compressor, which is a component constituting a freezing system such as a refrigerator, etc., serves to phase-shift low-temperature low-pressure gas refrigerant into high-temperature high-pressure gas refrigerant. Such phase shift can be implemented by a compressive force of a piston linearly reciprocated in a cylinder.
FIG. 1 is a view of an example of a conventional hermetic compressor, and FIG. 2 is a graph of the noise and the refrigerant velocity in the example of the conventional hermetic compressor.
As illustrated in FIG. 1, in the conventional hermetic compressor, a given lower container 1a and a given upper container 1b are coupled to constitute a hermetic container 1, a motor mechanism unit 4 composed of a stator 2 and a rotor 3 is installed in the hermetic container 1, and a plurality of compression components are installed on the upper side of the motor mechanism unit 4. A plurality of springs S are supported on the lower side of the stator 2 to absorb shock applied to the stator 2 during the rotation of the rotor 3, and components for transferring power are installed between the motor mechanism unit 4 and the compression components.
The components for transferring power include a rotational shaft 5, a cylinder block 6, a sleeve 7 and a connecting rod 8. The rotational shaft 5 is press-fit into a press-fit hole 3a penetrating through the center of the rotor 3 in the vertical direction and rotatably inserted into the cylinder block 6. An eccentric portion 5a provided at a top end portion of the rotational shaft 5 is coupled to the sleeve 7, and the connecting rod 8 converting a rotational motion into a linear motion is coupled to the sleeve 7.
The compression components include a cylinder 9 and a piston 10. The cylinder 9 is provided at one side of an upper portion of the cylinder block 6, and the piston 10 is inserted into the cylinder 9 and connected to the connecting rod 8 to be linearly reciprocated. Here, a valve device 11 for use in sucking/discharging refrigerant gas into/from a compression space of the cylinder 9 is coupled to an one-side opening portion of the cylinder 9, and a head cover 12 partitioned into a suction space and a discharge space to separate suction refrigerant from discharge refrigerant is coupled to the outside of the valve device 11. In addition, a suction muffler (not shown) is coupled to the lower side of the head cover 12 to communicate therewith. The suction muffler communicates with a suction pipe 14 provided in the hermetic container 1 via a connector (not shown). Moreover, a discharge muffler (not shown) for reducing the noise of discharge refrigerant may be provided on the upper side of the head cover 12 to communicate therewith. The discharge muffler communicates with a discharge pipe 15 provided in the hermetic container 1 via a loop pipe 16.
The operation of the hermetic compressor will be described. When power is applied to the motor mechanism unit 4, the rotor 3 is rotated due to the interaction between the stator 2 and the rotor 3, and the rotational shaft 5 coupled to the rotor 3 is rotated. As the rotation of the rotational shaft 5 is converted into a linear reciprocating motion by the connecting rod 8, the piston 10 is linearly reciprocated in the compression space in the cylinder 9. Here, when the piston 10 moves backward, refrigerant is introduced into the valve device 11 through the suction muffler and the suction space of the head cover 12 via the suction pipe 14. When a suction valve (not shown) of the valve device 11 is open, the refrigerant is sucked into the compression space in the cylinder 9.
Thereafter, when the piston 10 moves forward, the refrigerant compressed in the compression space opens a discharge valve (not shown), is discharged into the discharge space of the head cover 12, and is discharged to the outside through the discharge pipe 15 of the hermetic container 1 via the discharge muffler and the loop pipe 16.
In the conventional hermetic compressor described above, the adhesion of the connector is designed to be higher than an inner pressure of the suction pipe such that the elastic connector is closely attached to the inside of the hermetic container. Therefore, even if the refrigerant varies, the inner pressure of the suction pipe is maintained relatively low. For example, in the case of a hermetic compressor using refrigerant 600a, a suction pressure Ps is maintained at −0.43 kgf/cm2, which is a negative pressure (− pressure), and in the case of a hermetic compressor using refrigerant 134a, a suction pressure Ps is maintained at 0.14 kgf/cm2, which is a low positive pressure (+pressure).
Accordingly, in the conventional hermetic compressor, since the suction pressure is significantly lower than the pressure of the compression space, as shown in FIG. 2, the refrigerant suction velocity is high (9 m/sec2), but the refrigerant noise in specific frequency bands such as 4 k is high (about 28 dBA). As a result, there is a need to improve noise performance.